A plane passenger whose leg 'snapped in half' when the aircraft was hit by turbulence as he was returning from the toilet had to endure six hours of agony  before it reached its destination.

Niko broke two bones in his leg just 30 minutes into a seven-hour flight from Bali to New Zealand on Tuesday.

Niko and Sasha, a German couple who have been living in Bali for 13 years, flew with Air New Zealand from Denpasar to Auckland for the start of a planned month-long holiday.

All that changed when the plane encountered turbulence and suddenly 'dropped' as Niko was walking back to his seat.

A friend who was waiting to pick the couple up from the airport said he fractured his tibia and fibula in the incident.

Niko (pictured) was transported to Middlemore Hospital with a fractured tibia and fibula

'His leg pretty much snapped in half,' the friend told The New Zealand Herald. 

As the plane continued to Auckland, Niko endured six-and-a-half hours of agony with only Panadol to slightly ease the pain.

'Crew asked some passengers to move from their seats so he was able to lie down for the remainder,' his friend said. 

It is understood that the pilot later came out of the cockpit to check on passengers after the severe turbulence. 

Hato Hone St John paramedics were waiting at the international terminal to treat Niko when the plane landed at 5.40am on Wednesday. 

He was then transported to Middlemore Hospital. 

Air New Zealand confirmed the incident occurred when the plane encountered 'clear air turbulence'.

This is severe wind turbulence which occurs in cloudless regions that pilots are unable to see and radars do not detect, causing violent buffeting of an aircraft.

Niko and Sasha, a German couple who have been living in Bali for 13 years, boarded an Air New Zealand flight from Denpasar to Auckland on Tuesday night

Air New Zealand Chief Operational Integrity and Safety Officer, Captain David Morgan told Daily Mail Australia that one passenger sustained an injury on NZ65.

'In the event of a medical incident onboard an international service, our crew will contact Flightcare Global, our international medical support, who provide advice and recommendations based on the information they receive,' he said. 

'Depending on the situation, crew may put a call out to see whether there is a doctor onboard. If there is a doctor available who can support the passenger, our crew will take guidance from them in conjunction with Flightcare Global.

'If operationally viable, an aircraft will divert if Flightcare Global is sufficiently concerned about the individual's immediate welfare and determines that further medical attention is immediately required. 

'They will also consider factors like the level of medical care likely available to the individual in the possible diversion locations and whether it is in the individual's best interest to continue to the intended destination.

'The safety and wellbeing of our customers and crew is our number one priority. Our crew are trained to respond to medical emergencies and always prioritise the wellbeing of the customers onboard the aircraft.'